The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Controlling the amount of fuel and air to be delivered per cylinder for a four stroke internal combustion engine is important to achieve optimum performance. Proper timing of intake and exhaust valves also provide for better performance. Conventional engines include camshafts that regulate the timing of the valves. The rotation of the camshaft can be controlled to ensure proper timing of each valve. In addition cam phasers may be included to alter the position of the camshafts relative to the crankshaft, which provides for further opportunities to properly adjust the timing of each valve.
The placement of fuel injectors within the engine and the control of fuel injection timing also impacts engine performance. Spark-ignited direct injected (SIDI) engines locate one fuel injector per cylinder, mounted directly over the cylinder head. Each injector is controlled individually to inject fuel directly into the cylinder.
Conventional methods of controlling fuel during idle conditions in a SIDI engine include intentionally retarding the spark timing in order to provide a reserve torque. Spark timing is then advanced when a request for torque is initiated. This allows the engine to respond to load demands during idle operation. Retarding spark at idle provides for sub-optimal efficiency.
Other methods of fuel injection control include delivering multiple fuel injection events per cylinder per combustion cycle. A direct injection engine may use two injection events per cylinder per combustion cycle in special operation regimes to provide additional energy for converter lightoff, a smooth idle, and reduce engine knock. Unfortunately, the dual injection mode of operation produces higher hydrocarbon emissions and particulates. Accordingly, engine control may primarily include providing one injection event per cylinder per combustion cycle for emissions reasons. The dual injection method may be sparingly used for special operation regimes.
Dual injection per cylinder per combustion cycle generates more or less engine torque than a single injection mode within the same engine at similar operating conditions. Accordingly, drivability may be affected by sudden engine output torque changes during periods when the fuel delivery mode changes from a single to a multiple injection mode and vice versa.